It will be appreciated that load-dependent braking arrangements have been previously proposed, such as, the automatically load-dependent brake pressure control device shown and disclosed in published German Patent Application DE-PS No. 27 03 945, which corresponds to British Pat. No. 1,548,838 of the above-noted patent.
Referring now to FIG. 3 in comparison to FIG. 1, it will be noted that the seal element or O-ring is missing. This load-braking force regulator delivers a brake pressure determined for the brake cylinders of one or more vehicle axles in relation to a control pressure originating from a brake valve. The pressure is not reduced in an initial entrance phase; and in subsequent control phase, the pressure is dependent upon a ratio which is a function of the load status of the vehicle, namely, the control ratio.
The control is carried out by means of a control valve which is activated by a control piston having a control surface pressurized by the control pressure and a reaction surface pressurized by the brake pressure. The size of the reaction surface can be varied as a function of the load. The reverse side of the reaction surface forms a variable accessory surface which is located adjacent to an accessory chamber which, together with the control surface, always has essentially the same size as the reaction surface.
In the entrance phase, both the control surface and the accessory surface are pressurized with the control pressure, and as a result the brake pressure is delivered unchanged in relation to the control pressure. After a predetermined entrance pressure is reached, the entrance device prevents any further increase of the pressure in the accessory chamber. The further increase of the brake pressure in the subsequent control phase is a function of the ratio of the surface areas between the reaction surface and the control surface which varies with the size of the reaction surface, also as a function of the load.
The family of characteristic curves of this load-dependent brake force consists in the control phase of a family of control lines which always correspond to a load status of the vehicle.
There are applications for vehicles in which, for example, on account of government regulations, it is necessary in emergency situations that the brake pressure in the vehicle must be able to increase in stages up to the full available delivery or supply pressure. Since on vehicles with load-dependent brake devices, the type of brake pressure mentioned above cannot increase beyond that which corresponds to the load status, this requirement can be met on vehicles equipped in this manner only if additional separate valve and/or equipment is used as adjunct.